This disclosure generally relates to actuators for flight control surfaces and, in particular, relates to jam-tolerant systems for actuating flight control surfaces.
Deployable leading and trailing edge devices have been used for many years to control the attitude and lift/drag characteristics of modern aircraft. In particular, conventional trailing edge ailerons located on left and right aircraft wings are deployed asymmetrically to roll the aircraft. Trailing edge flaps are generally deployed symmetrically to create high-lift wing configurations suitable for landing and take-off. The flaps are then stowed for more efficient operation at cruise conditions. Conventional trailing edge devices typically include flaps, ailerons, or flaperons that are hinged relative to the wing, and are driven between stowed and deployed positions by one or more actuators.
Movement of aircraft control-surface components is crucial in flight, whereby an actuating assembly must consistently and dependably perform during normal operation. In particular, it is desirable that a flight control surface continue to be deployable even if the actuator assembly becomes jammed due to an obstruction. The definition of jam tolerance encompasses the ability of an actuator, or an actuator system, to permit continued input drive capabilities in the event of a jam in the actuator, or one or more of the actuators in an actuator system, respectively, resulting from an obstruction or internal actuator failure. In the context of the aerospace industry, such a jam-tolerant feature permits continued aircraft control flap movement in the event of a jam in one or more of the actuators in an actuator system.
Regulations require that an airplane be shown by analysis, tests, or both, to be capable of continued safe flight and landing after any one of a number failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems), within the normal flight envelope, without requiring exceptional piloting skill or strength. Any jam in a control position normally encountered during takeoff, climb, cruise, normal turns, descent, and landing must be accounted for. In particular, the aircraft cannot have an undetected failure in a control surface prior to the next flight, loose functionality, departure of a component from the airplane, or collateral damage locally or downstream.
A known flaperon assembly (see, e.g., U.S. Pat. No. 7,766,282) comprises a flaperon linked by linkage mechanisms to a wing and a rigid panel coupled by hinges to the wing and linked to the linkage mechanisms for coordinated panel rotation and flaperon movement. The flaperon assembly further comprises a pair of unitary cam track assemblies attached to the wing by respective brackets, each cam track assembly comprising a pair of cam surfaces (a.k.a. “cam tracks”). One cam surface is a failsafe feature which provides redundancy for the flaperon and does not carry any flight or system-generated loads. The other cam surface provides the program position for the rigid hinged panel. Due to linkage mechanism movement and the trapped programming tracks (i.e., cam surfaces) in this type of flaperon assembly, it is possible for an obstruction to occur. The obstruction can occur within the mechanism movement, in the cam track or surface, or in a pinching jam between moving and stationary parts.
There is a need to relieve or prevent the obstruction without jeopardizing the functionality of the linkage mechanisms, thereby avoiding unacceptable collateral damage and parts departing the airplane. In addition, the damage resulting from the obstruction must allow the mechanism to be functional without further degradation until planned maintenance inspection.